Sandwich Construction

Sandwich construction refers to a door section built from three bonded layers: an outer steel skin, a core of foam insulation, and an inner steel or vinyl backer panel. Amarr describes the concept as "Triple-Layer: Steel + Insulation + Steel Interior." The term comes from the way the foam is captured between two rigid face materials, like a filling between two slices of bread.

There are two main ways to build a sandwich section. In the first method, polyurethane foam is injected in liquid form between the already-assembled outer and inner skins. The foam expands and cures, bonding to both surfaces and adding structural rigidity to the section. In the second method, a pre-cut polystyrene board is inserted into the cavity after the steel frame is formed, and the inner liner is then attached.

The injected polyurethane method produces a stronger bond and higher R-values for the same foam thickness. The inserted polystyrene method is less expensive and commonly found on mid-range residential doors.

A sandwich door section is stiffer than a single-skin section of the same steel gauge. The insulation core resists denting and reduces sound transmission from the street into the garage. It also reduces thermal conduction compared to a bare steel panel.

The thermal break at the edges of the section prevents the outer and inner steel skins from conducting heat directly to each other around the perimeter of the foam. Without it, the steel edges bridge the insulation and reduce the effective R-value of the door.

Single-skin steel doors are sometimes called "pan doors" in commercial use: one formed steel sheet with hollow sections and no insulation.